According to xbox.com, the 1600 and 4000 points purchased from the U.S. can only be applied to accounts registered to the U.S.
The points is compatible with USA Xbox 360s only and USA Xbox Live Accounts on non USA based Xbox 360s. Example: If you are based in England, but have a USA Xbox Live account on your 360, the code will work for you. We have satisfied customers from around the world. The Gold Subscription code, however, works worldwide.